1. Field of Invention
The present invention relates to a pedal simulator of a brake apparatus for a vehicle, and more particularly, to a pedal simulator which can minimize increases in an entire length of a spring and a volume of a cylinder even if a plurality of springs in a multi-stage series form.
2. Description of Related Art
In general, a brake apparatus for a vehicle is adapted to slow or stop a traveling vehicle or maintain the stopped state of the vehicle, and a braking operation is performed by converting kinetic energy of the vehicle into thermal energy due to mechanical friction and dissipating the frictional heat into the air.
Such brake apparatuses for a vehicle include drum type hydraulic brakes and disk type hydraulic brakes. Among them, a disk type hydraulic brake strongly presses a disk rotating together with a wheel at opposite sides with a friction pad instead of a drum to obtain a braking force.
However, the hydraulic brake has a complex structure due to a mechanical element connected to a brake pedal, a hydraulic pressure pipe, and an element for controlling a hydraulic pressure.
Thus, electro-mechanical brakes (EMBs) are being recently developed and used to simplify the configuration thereof.
Such an electro-mechanical brake refers to a brake for pressing a friction pad by using a mechanical structure driven by an electric motor to obtain a braking force unlike a general hydraulic brake.
An electro-mechanical brake includes an actuator having a motor rotated forwardly and reversely to perform a braking operation or releasing the braking operation, and presses the friction pad by using a rotating force of the motor to press a disk (generate frictional with the disk).
Further, the electro-mechanical brake receives a brake intention of a driver through a brake pedal and adjusts braking pressures of front and rear wheels by using a motor.
The electro-mechanical brake is a new-generation brake concept, and is expected to be applied to an environment-friendly vehicle such as an electric vehicle as it has a quick response speed and enables a precise control as compared with a hydraulic brake.
The electro-mechanical brake may be realized by a system combined with a hydraulic brake, and for example, a hydraulic brake is applied to a front wheel and an electro-mechanical brake is applied to a rear wheel, which has a simple structure, has an excellent braking response, and provides an easy control as compared with a system employing only a hydraulic brake according to the related art.
A brake-by-wire (BBW) system in which the electro-mechanical brake is mounted to all the front and rear wheels of a vehicle may be realized, and electric calipers located at the front and rear wheels hold a disk in response to a signal of a control unit to brake the vehicle.
The BBW system transfers a braking intention of a driver by using an electric signal, in which system a mechanical connection is not present between a brake pedal and the wheels, braking forces for the wheels can be independently controlled precisely, and a braking force can be easily controlled to shorten a brake distance, and a braking stability can be increased.
An electronic hydraulic brake (EHB) as another form of the BBW system is a system is a system for allowing a control unit to receive a pedal travel sensor and a signal of a hydraulic sensor in a master cylinder during a braking operation to recognize a braking intention and a required reduction speed, and control a hydraulic pressure of a high-pressure accumulator through a solenoid valve to hydraulically brake the wheel.
Meanwhile, the electro-magnetic brake includes a pedal simulator for providing a pedal feeling such as a hydraulic pressure by using hysterisis characteristics.
The pedal simulator is an apparatus for realizing a pedal feeling like that of a hydraulic brake according to the related art when a driver steps on a pedal, and a brake pedal force of a driver is formed by using the pedal simulator and a braking operation of the driver is supplemented by transferring a proper pedal reaction force to the driver.
The pedal simulator may be variously configured, but includes a cylinder into which an operation rod coupled to a pedal and moved forward and rearward along a stroke of the pedal, and a piston resiliently supported by a spring in the cylinder and moved by the operation rod.
Here, in describing various examples of the configuration for realizing a pedal force, FIGS. 1 to 4 illustrate known pedal simulators 1. A configuration of FIG. 1 in which a plurality of cylinders 6 and 7 in which springs 6b and 7b are installed are connected to a hydraulic cylinder 4 in parallel through a hydraulic pipe 5, and a configuration of FIG. 2 in which a hydraulic cylinder 4 employing a spring 4b therein and a separate cylinder 6 employing a spring 6b therein are connected to each other through a hydraulic pipe 5 are known.
In the configuration of FIG. 1, if a driver steps on a pedal 2, an operation rod 3 is moved to press a piston 4a in a first cylinder 4, and the oil in the first cylinder 4 is sent to a second cylinder 6 and a third cylinder 7 connected to each other in parallel as the piston 4a is moved.
Further, the second cylinder 6 and the third cylinder 7 are provided with pistons 6a and 7a and springs 6b and 7b, and when the oil is distributed from the first cylinder 4, the pistons 6a and 7a are moved. Then, the springs 6b and 7b are pressed to generate reaction forces.
In addition, in order to realizing a pedal feeling, a configuration of FIG. 3 in which a plurality of springs 8b and 8c disposed to support a piston 8b in series are installed in one cylinder 8 and a configuration of FIG. 4 in which a spring 9b and a rubber member (cushion rubber) 9c as resilient members for supporting a piston 9a are combined in one cylinder 9 are known.
In order to secure a displacement necessary for a spring, an entire length of a spring is determined, considering a wire diameter, an effective displacement for securing durable strength, and the like of FIG. 5, and accordingly, as illustrated in FIG. 3, when several springs 8b and 8c are disposed in series, a sum of the spring lengths becomes still larger than the actually necessary displacement, significantly increasing the necessary entire length.
Further, as illustrated in FIG. 6, if the springs 11 are disposed in parallel, a spring mounting space increases.
When a pedal force is generated by using a spring in a general pedal simulator, several springs cannot be used by the spatial restriction, and a pedal simulator having two step inclinations by generally using two springs is configured as in FIG. 3.
However, it is difficult to simulate proper reaction force characteristics of a brake pedal with the two step inclinations, and in comparison with a pedal force generation pattern of a general vehicle as in FIG. 7, a portion different from a general vehicle as indicated by a dotted line is generated when the stroke-pedal force pattern of a general vehicle is simulated with two springs.
Further, as illustrated in FIG. 4, when a rubber member 9c is combined to be used, the stroke-pedal force characteristics vary as the characteristics of the rubber vary according to a temperature change (the stroke-pedal force characteristics vary when a temperature is high and low).
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.